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<TITLE>More Cascade Union Adventures</TITLE>
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<P><FONT SIZE=2>Martin,<BR>
<BR>
PostGIS just may beat JTS by cheating a little. I think I have managed to up one on Kevin's solution by cheating. One of the PostgreSQL developers pointed out to me that array_append is highly inefficient and testing out the st_geom_accum - that suffers from similar issues. Watch these tests. I tested on OpenJump too and got 55 second response. Of course that was not a fair test since my workstation does not have PostgreSQL on it. I'll have to wait till later when I'm at a box that has both PostgreSQL and OpenJump installed to do a fair comparison.<BR>
<BR>
I also remarked out the sorting I was doing because it didn't seem to be consistently better in all cases.<BR>
---THE TESTS ---<BR>
-- 231,312 ms = 3.85 mins - SELECT 231312/1000.00/60<BR>
SELECT ST_CascadeUnion(the_geom)<BR>
FROM (SELECT * FROM sample_poly) As foo;<BR>
<BR>
--44,453 ms = 45 secs = wow! SELECT 44453/1000.00<BR>
SELECT st_unitecascade_garray_sort(ARRAY(SELECT the_geom FROM sample_poly));<BR>
<BR>
-- 77,078 ms, 75124 ms = 1.26 min<BR>
SELECT ST_NumGeometries(ST_Union(the_geom)) AS the_geom<BR>
FROM (<BR>
SELECT min(id) AS id, ST_Union(the_geom) AS the_geom<BR>
FROM (<BR>
SELECT min(id) AS id, ST_Union(the_geom) AS the_geom<BR>
FROM (<BR>
SELECT min(id) AS id, ST_Union(the_geom) AS the_geom<BR>
FROM (<BR>
SELECT min(id) AS id, ST_Union(the_geom) AS the_geom<BR>
FROM (SELECT * FROM sample_poly) As foo<BR>
GROUP BY round(id/10)<BR>
ORDER BY id) AS tmp1<BR>
GROUP BY round(id/100)<BR>
ORDER BY id) AS tmp2<BR>
GROUP BY round(id/1000)<BR>
ORDER BY id) AS tmp3<BR>
GROUP BY round(id/10000)<BR>
ORDER BY id) AS tmp4<BR>
GROUP BY round(id/100000);<BR>
<BR>
<BR>
-----THE CODE ---<BR>
<BR>
CREATE OR REPLACE FUNCTION st_unitecascade_garray(geometry[], iter int,<BR>
startcount int)<BR>
RETURNS geometry AS<BR>
$$<BR>
SELECT CASE WHEN array_upper($1,1) < 5 OR array_upper($1,1) BETWEEN 0<BR>
AND ln($3 + 1)/ln($2 + 1) THEN st_unite_garray($1) ELSE<BR>
st_unitecascade_garray(ARRAY(SELECT st_unite_garray($1[i:least(i<BR>
+ CAST(ln($3 + 1)/ln($2 + 1) As int) - 1,array_upper($1,1))]) As geom<BR>
FROM generate_series(1, array_upper($1,1), CAST(ln($3 + 1)/ln($2 + 1) As<BR>
int)) As i), $2 + 1, $3) END<BR>
<BR>
$$<BR>
LANGUAGE 'sql' IMMUTABLE;<BR>
<BR>
CREATE OR REPLACE FUNCTION st_unitecascade_garray_sort(geometry[])<BR>
RETURNS geometry AS<BR>
$$<BR>
SELECT CASE WHEN array_upper($1,1) < 10 THEN<BR>
st_unite_garray($1) ELSE<BR>
st_unitecascade_garray(ARRAY(SELECT ($1)[s] FROM<BR>
generate_series(1, array_upper($1, 1)) AS s<BR>
--ORDER BY ST_SnapToGrid(ST_Centroid(($1)[s]),0.1)<BR>
) , 2, array_upper($1,1)) END;<BR>
$$<BR>
LANGUAGE 'sql' IMMUTABLE;<BR>
<BR>
--DROP AGGREGATE st_cascadeunion(geometry);<BR>
<BR>
CREATE AGGREGATE st_cascadeunion(geometry) (<BR>
SFUNC=st_geom_accum,<BR>
STYPE=geometry[],<BR>
FINALFUNC=st_unitecascade_garray_sort<BR>
);<BR>
<BR>
<BR>
<BR>
<BR>
--BEGIN TESTS --<BR>
CREATE INDEX idx_sample_poly_the_geom<BR>
ON sample_poly<BR>
USING gist<BR>
(the_geom);<BR>
<BR>
<BR>
ALTER TABLE sample_poly CLUSTER ON idx_sample_poly_the_geom;<BR>
CLUSTER sample_poly;<BR>
<BR>
<BR>
vacuum analyze sample_poly;<BR>
<BR>
<BR>
Thanks,<BR>
Regina<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
<BR>
</FONT>
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